Expansion Tanks

Sizing an expansion tank.

Expansion tanks are used to control the water system pressure in radiant heating, hydronic heating and domestic plumbing, which is caused by the expanding hot water. As water becomes hot, it expands. When water expands, it greatly increases the pressure in your system. If that pressure isn’t relieved, the system start leaking, or it may even rupture from too much pressure. Expansion tanks are used to reduce that pressure, by providing the extra room needed for the excess water.

For domestic plumbing, you will need Therm-X-Trol expansion tanks.

For radiant heating and hydronic heating applications you will need Extrol, Radiant Extrol, or Fill-Trol expansion tanks.

Oversizing and undersizing

Before purchasing an expansion tank, you have to consider if that expansion tank can handle system needs. If the tank is undersized, the excess pressure from the expanding water will release the pressure valve.  If you’re not completely sure your selected expansion tank can safely handle the system pressure, it’s best to purchase an expansion tank which is one size bigger than the requirements. There is no disadvantage to having a larger than the minimum required expansion tank. It is best to oversize than undersize.

Heating

Extrol and Fill-Trol expansion tanks

Extrol and Fill-Trol are the basic types of expansion tanks used. When it comes to closed-loop hydronic heating and radiant heating, Extrol expansion tanks are the most common expansion tanks used for heating applications. Fill-Trol expansion tanks are similar to the Extrol tanks, however, Fill-Trol tanks include an automatic, pressure-reducing fill valve, so there is no need to purchase and install a separate fill valve. When choosing the right size, look at the BTU’s per hour the boiler outputs. The BTU’s/hr are usually displayed on the boiler itself.  The Fill-Trol expansion tanks are sized the same way as the Extrol tanks and use similar models.

Extrol expansion tank

  • Eliminates air trapped in the system from Amtrol’s automatic air vent
  • Controls and reduces water pressure in the system.
  • Uses Butyl/EPDM diaphragm, which retains any air from escaping the tank much better than natural rubber.
  • Has both in-line and floor mounted models applicable for any radiant heating, hydronic heating, or domestic plumbing system.
  • Installed easily

Fill-Trol expansion tank

  • Has the same great features as the regular Extrol expansion tanks.
  • Provides accurate and total control of the pressure in the system.
  • No need to purchase a separate automatic fill valve, Fill-Trol has one built in.

Note: Extrol models 15, 30, 60, and 90 are similar to Fill-Trol 109, 110, 111, and 112 respectively.

Fill-Trol models are in bold.

Extrol & Fill-Trol expansion tank sizing

Boiler output in 1000’s of BTU’s/hr
Heating types 25 50 75 100 125 150 175 200 250 300 350 400
Radiant heating 15 109 15 109 30 110 30 110 30 110 30 110 60

111

 60

111

 60

111

 90

112

 SX30V SX30V
Copper baseboards 15 109 15 109 30 110 30 110 30 110 30 110 60 111 60                                  111 60      111 90      112 SX30V SX30V
Cast-iron baseboards 15 109 30 110 60 111 60 111 90 112 90 112 SX30V SX30V SX40V SX40V SX60V SX60V
Convectors/ Unit-Heaters 15 109 15 109 30 110 30 110 60 111 60 111 60       111 60   111 90   112 SX30V SX30V SX40V
Cast-iron radiators 15 109 30 110 30 110 60 111 60 111 90

112

 SX30V SX30V SX30V SX30V SX40V SX40V
Models

Radiant Extrol expansion tanks

Radiant Extrol expansion tanks are also used in radiant heating, however, they differ from Extrol and Fill-Trol because they can be used for closed-loop heating and also with your domestic hot-water plumbing system. Radiant Extrol expansion tanks are commonly used in open-loop heating applications where high oxygen content can lead to rust and corrosion. Radiant Extrol tanks are made with non-ferrous materials which provide greater corrosion resistance. They can also be used for snow melting applications using a glycol/water mix. The size of the models you would need depends on the length of PEX tubing and the inner diameter of the tube.

Radiant Extrol expansion tanks

  • Compatible with both oxygen-barrier PEX tubing and non-barrier
  • Made with non-ferrous materials to withstand systems with higher oxygen content
  • Suitable to be used in snow melting applications with glycol/water mix

Radiant Extrol expansion tanks

Length of tubing in Ft.
Pex tubing size 1,000 5,000 7,500 10,000 14,000 18,000 22,000 30,000
3/8″ RX-15 RX-15 RX-15 RX-15 RX-15 RX-30 RX-30 RX-30
1/2″ RX-15 RX-15 RX-15 RX-30 RX-30 RX-60 RX-60 RX-60
5/8″ RX-15 RX-15 RX-30 RX-30 RX-60 RX-60 RX-60
3/4″ RX-15 RX-30 RX-30 RX-60 RX-60 RX-60
1″ RX-15 RX-30 RX-60 RX-60
Models

Plumbing

Therm-X-Trol expansion tanks

Therm-X-Trol expansion tanks are used in domestic water systems. This type of expansion tanks are used to lower the pressure in your plumbing system, which is caused by the expanding hot water. The pressure from the expanding water can cause the relief valve open resulting in a waste of energy, property damage, and a possible safety risk. Installing a Therm-X-Trol expansion tank can protect you from any problems that may ocure in your domestic water system. These expansion tanks are sized by the capacity the water heater can hold (Gallons) and the static supply pressure (PSI) in the system.

Therm-X-Trol expansion tanks

  • Reduce the risk of the relief valve opening.
  • Controls system pressure and helps reduce it.
  • Installs easily
  • Made with quality materials

Maximum system temperature 150*F

Static supply pressure (psi) Water heater size (Gallons)
40 50 60 80 120
40 ST-5 ST-5 ST-8 ST-8 ST-12
60 ST-5 ST-5 ST-8 ST-8 ST-12
80 ST-5 ST-8 ST-8 ST-12 ST-25V
Models

Aquastat set up to 180*F

Static supply pressure (psi) Water heater size (Gallons)
40 50 60 80 120
40 ST-8 ST-8 ST-8 ST-12 ST-12
60 ST-8 ST-8 ST-12 ST-25V ST-25V
80 ST-8 ST-12 ST-25V ST-25V ST-25V
Models